The present invention relates to a medical, bioresorbable implant, a process for its production and its use in medicine.
Artificial implants are generally used in surgery as means for fixing, supporting or replacing diseased or injured body parts. For example, surgical sutures, replacements for tendons and ligaments and vascular prostheses are known.
Artificial implants in the form of cords or bands have been specifically developed for applications in orthopedic surgery for humans and animals. A typical example of the use thereof is a cruciate ligament rupture, where an implant is useful in reconstruction or as a prosthesis.
As implants of non-resorbable materials suffer from significant disadvantages, such as e.g. foreign body reactions and an infection tendency, implants of partly or completely resorbable material have been developed. The Ethicon DE-A1-19613730 discloses a flat or areal implant of not or only slowly resorbable material, which is stiffened with a further, rapidly resorbable material. Various degradable implants based on alpha-hydroxycarboxylic acid polyesters are also known. In DE-C2-4012602, Ethicon discloses polydioxanone cords.
Particularly in applications where the implant is only intended to temporarily exercise its function until the endogenic tissue has recovered, it is desirable for the inserted implant to gradually lose its mechanical stability and consequently increasingly transfer the load to the tissue to be restored.
In practice the known implants suffer from the disadvantage that during the degradation phase, following an initial softening, an embrittlement occurs, which reduces the extensibility of the implant and either leads to an undesired extension restriction or to premature implant fracture. The functional loading is only taken over in the known implants by the endogenic tissue to be restored when the implant material has degraded to such an extent that implant fracture occurs.
The problem of the invention is consequently to make available a medical, bioresorbable implant, particularly an augmentate, which has in vivo the desired mechanical characteristics together with an advantageous biological degradation and resorption behaviour, which is simple and inexpensive to manufacture and which is easy and reliable during use for implantation purposes during surgery.
This problem is solved by a medical, bioresorbable implant, particularly for cruciate ligament augmentation, constructed as a composite structure with a textile construction from at least two biocompatible polymer materials, which differ in their chemical composition and/or polymer structure and which are degradable, the implant having a predetermined initial tensile stiffness and a differing degradation behaviour of the polymers and/or the textile construction is selected in such a way that the tensile stiffness decreases during degradation.
The implant is particularly constructed as an augmentate for cruciate ligament augmentation. As a result of the decrease of the tensile stiffness of the implant, increasingly the load is transferred to the tissue to be restored.
In this connection stiffness is a measure of the resistance to shape changes. It can be represented as an increase in the force pattern over the displacement. It is also related to the modulus of elasticity, which additionally takes account of the starting cross-section and starting length of the sample material.
In the biological resorption of natural or synthetic polymer materials in a physiological environment, there is firstly a degradation of the polymer chains, followed by a further decomposition of the degradation products and finally the substance mass is resorbed. A decrease in the tensile stiffness of the polymer can occur during degradation, but at the latest during the resorption of the decomposition products.
In a special embodiment a medical, bioresorbable implant is made available, which is constructed as a composite structure in textile construction from at least three or more, biocompatible polymer materials, which differ as regards their chemical composition and/or polymer structure and which are degradable, the implant having a predetermined initial tensile stiffness and a differing degradation behaviour of the polymers and/or the textile construction is selected in such a way that the tensile stiffness decreases during degradation. As a rule two or three different polymer materials are sufficient.
With particular advantage the implant according to the invention is characterized in that all the polymers are completely resorbable.